See this post …
Names of components in local folder does not match names in the component window
Do the above first, by creating a folder in your “user” Materials path, and add the .skm files into the new folder. You may need to restart SketchUp for the new folder to be enumerated, but you can try changing the folder in the Materials inspector panel and back again to see if the user “Materials” folder is re-enumerated.
Once you see the materials listed you can select them and the Paint Bucket tool should be activated.